I'v had a '99 A4 Jetta TDI since new, and I like it a lot. It handles better (sportyer) than any car I have had before.
The older engines are made in Germany, I am not sure about the new PD TDI's. The older TDI's with the VE pumps will last a long time if you tend to the maint like they suggest. One problem that has come up is the MAF sensor sometimes goes bad. I have had one go out on mine.
Timeing belt change out interval depends on the year and type of transmission and the belt. Auto transmissions originaly were 40k miles, and 60K miles for manuals. Later engines, with different belts, it was 80 and 100K miles. If buying used, check to see if the belt has been changed if the miles are such that it should have been done.
I am not sure on the new PD engines what the interval is.
I have a friend at work with a '00 Jetta automatic, who is over 150k miles on his car. At the 120K mile belt change he changed out the water pump, as it is run off the t'belt as a precaution. . Cheap insurance!
If the EGR is still intact on a used car, you might be looking at cleaning the intake, as they will tend to crud up rather badly. The oily CCV vapor and the EGR soot make a real mess in the intake manifold.
With EGR non- functional, there will be very little gunk in the intake, but you will most likely get a CEL on the dash board. There are ways around this (for educational purposes only!

)
Lots of info available (probably info overload) about t-belts and how to, MAFS and just about anything else at
www.TDICLUB.COM
Drive ON!